1. Field of the Invention
The present invention pertains to methods for efficient data storage and more particularly to methods for reducing the amount of storage space needed by compressing the data to be stored.
2. Related Prior Art
In general, prior art makes use of the entire data set and compresses the data according to various individual methods. This compression normally takes the form of sequentially deleting samples in a predetermined manner.
U.S. Pat. No. 4,121,191, "Seismic Data Tape Recording System," (Corkhill), relates to an apparatus for increasing the seismic data storage capacity of magnetic tape. A pair of storage registers store a sequential pair of digitized seismic data samples. A subtractor coupled to these two registers provides an output equal to the difference between the two stored samples. A decoder and a set of gates couples the difference word serially to a bit comparator starting with the most significant bit. The first logical "1" which is encountered and all the lower order bits of the same word are serially coupled to and written in a read/write memory. The decoder and gates cause a "0" to be written in a second read/write memory at the beginning of each data word, and "1's" to be written in addresses corresponding to the data written in the first read/write memory. The data in the read/write memories are addressed for reading by a read/address counter, which is incremented by an incremental shaft encoder on a drive motor of a tape recorder. An up-down counter continuously monitors the difference between the number of bits written into the read/write memories and the number read from the memories and serially recorded by the tape recorder. The output of the up-down counter is used to control tape recorder motor speed. This patent relates to a data compression scheme in which a pair of storage registers store a sequential pair of digitized seismic data samples. A circuit coupled to the two registers provides an output equal to the difference between the two storage samples. A decoder and a set of gates are used to couple the difference word serially to a bit comparator starting with the most significant bit. In this reference, sequential pairs of data are stored, not mathematically folded data.
U.S. Pat. No. 4,509,150, "Linear Prediction Coding for Compressing of Seismic Data," (Davis) relates to a seismic data compression technique which comprises sampling each individual seismic trace, operating upon a set number of samples to generate a predicted sample and quantizing the difference between the next sample and the predicted value of the sample, and transmitting the quantum number whereby the amount of information which need be transmitted is limited. In a preferred embodiment, a linear prediction differential pulse code modulation scheme is used to provide the predicted value, while an adaptive quantization scheme is used to quantize the error value to be transmitted, thus yielding further improvements in accuracy. A feedback loop can be applied to the decompression operation to limit quantization noise and further improve the fidelity of representation of the decompressed signals. This patent relates to a data compression scheme which compresses data based on a sample taken of each individual seismic trace. A predetermined number of samples are used to predict a subsequent sample. The difference between the next sample and the predicted value of the sample is quantized. A linear prediction differential pulse code modulation scheme is used to provide the predicted value. An error value is also determined and transmitted. This scheme is closely related to adaptive predictive linear coding. It does not contain teachings or suggestion of folding the data nor the total elimination of a preselected section of data.
U.S. Pat. No. 4,543,648, "Shot to Shot Processing for Measuring a Characteristic of Earth Formations From Inside A Borehole," (Hsu). A method and apparatus for measuring an earth formation characteristic from inside a borehole penetrating earth formations is described. A tool carrying a sonic transmitter and an array of receivers is moved along the borehole and waveform signals from the receiver array are generated from repetitive operations of the transmitter. Sub-arrays of particularly related waveform signals relevant to a selected depth interval that is less in length than the aperture of the array are identified. Each sub-array of signals is then converted to a domain of signals composed of values of a coherence as a function of a range of values of a characteristic such as slowness. The converted signals are then combined so as to provide combined coherence values as a function of different values of the characteristic. One or several peaks of the combined coherence values are detected and determine the value of the characteristic for the selected depth interval. Similar processing is continued for other depth intervals. Independent measurements of the characteristic can be made with both receiver section and transmitter section processing and a borehole compensation technique is described. A fast processing technique for processing data of many sub-array waveforms is described. This patent relates to a method and apparatus for measuring earth formations. The relevance of this patent is found in its discussion of combining converted signals to provide combined coherence values as a function of different values of the characteristic. In this method, one or several peaks of the combined coherence values are detected to determine the value of the characteristic for preselected depth intervals. This reference contains no suggestion or teaching of the folding of data.
U.S. Pat. No. 4,715,002, "System for Recording a Variable Value, Notably in a Well, and For Compressing Stored Measurement Interval Data", (Vernon et al.) relates to a method for acquiring and recording the variation of a value such as a pressure as a function of a parameter such as time in a sonde lowered into a well. Pressure measurements are made at equal time intervals, these measurements are digitized and entered in a nonvolatile memory selectively so as to maximize the accuracy of the pressure variation reading during the measurement period, while minimizing the memory volume necessary for this purpose. The selection of the acquired measurements for their recording comprises a data compression stage in which are eliminated the measurements which do not correspond to a variation in the slope of the pressure-versus-time curve greater than a predetermined threshold. The data compression is effected in a buffer memory in which a deviation index is associated with each measurement. The deviation index is indicative of the time interval separating this measurement from the following one in the buffer memory. This time interval amounts to a number of elementary time intervals which is always a power of two. The exponent of this power is stored as the deviation index. This patent relates to a data compression method in which measurements that do not correspond to a variation in the slope of a pressure versus time curve greater than a predetermined threshold are eliminated. While this reference discusses the elimination of data, it must review a predetermined aspect of each piece of data.